The present invention concerns a method for cleaning the ink chamber of a printing unit, preferably a chamber in a doctor blade, where pressurised cleaning liquid is sprayed into the chamber through at least one cleaning nozzle.
The invention also concerns a system for cleaning an ink chamber of a printing unit, preferably a chamber in a doctor blade, including at least one cleaning nozzle through which pressurised cleaning liquid is sprayed into the chamber.
The invention furthermore concerns a cleaning nozzle for use in a chamber in a doctor blade, where pressurised cleaning liquid is injected into the chamber through at least one such nozzle.
The prior art comprises a method for supplying a printing unit with cleaning liquid for cleaning the ink chamber of the printing unit and other components after each colour printing. The printing unit includes an ink chamber, preferably in the form of a chamber in a doctor blade and a pumping unit with pumps for supply and return pumping of ink/cleaning liquid. The cleaning liquid is pumped into the ink chamber through inlet/outlet of the chamber. The printing unit also includes suction lances for disposition in tank for ink/cleaning liquid for sucking up or return pumping cleaning liquid/ink and connecting lines with shut-off and switching valves which are controlled by a control unit for establishing the following steps:                an operation step where ink is circulated through the chamber;        an emptying step where the chamber is emptied for ink which is pumped back to the ink tank;        a step where a small amount of cleaning liquid is injected via the nozzles in the chamber and together with the last amount of ink pumped back to the ink tank;        a cleaning step where the chamber at least once is circulated with cleaning liquid pumped into the chamber via inlets/outlets and which is circulated through the components of the printing unit;        a further cleaning step where the chamber is flushed with cleaning liquid which is injected via separate cleaning nozzles and which is circulated through the components of the printing unit;        a final step where the components of the printing unit is pumped free/emptied from cleaning liquid, after which an operation step may be initiated again.        
As the ink chamber is provided with cleaning nozzles, it is possible to establish a secure flushing of the chamber between different operation steps with a minimal consumption of cleaning liquid. This may reduce the time used for cleaning and reduce the consumption of cleaning liquid. If these cleaning nozzles are also used during the last part of an emptying step, the ink chamber will be partly cleaned already after the emptying step. The amount of cleaning liquid and the time used for the subsequent flushing step may hereby be reduced. Finally, the amount of cleaning liquid may be further reduced when the final step is a reversal of the pumps for emptying the components of the printing unit for cleaning liquid, so that it is stored in the cleaning tank and is ready for use at the succeeding flushing step.
The used pumping unit forms part of a printing unit with an ink chamber and includes pumps for supply and return pumping of ink/cleaning liquid from an ink tank and a cleaning tank, respectively, suction lances for placing in the tanks and connecting lines with shut-off and switch valves that are controlled by a control unit.
The prior art pumping unit may be a separate unit with its own control system. Hereby, it may very easily be adapted to new or existing printing units as it may only be connected with these via return and supply lines to the ink chamber. Alternatively, it will also be possible to make a pump unit as an integrated part of the printing unit so that control is performed by means of a control unit simultaneously controlling the printing process itself.
US 2003/0167949 also discloses a cleaning system for printing machines. In this application there is described a system where water or liquid is stored in a container which is pressurised by a common air supply system for the associated printing machine. This means that a low pressure system is used for pressurising the storage container. In order that the container can be used in common cleaning, it will have a relatively large volume. When a large volume is used together with low pressure, there will be a need for a relatively large and energy consuming pump in order to attain a capacity that enables cleaning with a series of short shots during a cleaning cycle.
Printing units are used extensively within the graphic industry for multi-colour printing. Often there is a need for rapid and simple shifting between different ink colours. This puts demands on rapid and efficient cleaning as well as there is also a requirement that a large part of the ink amount as possible is returned to an ink tank for use in a later printing. It is desirable to return the ink to the ink tank, partly for avoiding contamination of cleaning water and partly for saving material expenses.
Printing units may be used for flexographic printing, coating, offset printing or other kinds of printing, where ink is transferred to a printing roller via a unit comprising ink chamber/screen roller, or directly to a print carrier.
In order to utilise the printing unit as efficiently as possible, it is desirable to have a time of change between the various ink colours so that the changing may be performed as quickly and automatically as possible.
However, the system will not provide for a secure and efficient cleaning of the ink chamber but only flushing, as the pressure at which the cleaning liquid is injected into the pipe depends on the pump capacity in the moment of injection. A large pump capacity is required, typically about 20-40 l/s, for achieving efficient flushing. A large pumping capacity is need if a large pressure is to be maintained at the injection. In order to avoid pressure loss and thereby reduced injection pressure, it will therefore be necessary with relatively large dimensions in connecting lines and pipes. Insufficient cleaning entails risk of ink residue giving problems at a subsequent operation step with a new colour. In order to get sufficient capacity, a large space-consuming and energy-consuming cleaning unit connected with the chamber via thick lines is provided in the prior art systems. The pump capacity produces a system with inferior energy economy as the pump has to operate continuously at high pressure with large capacity to be ready for giving off short shots during a cleaning cycle.
The description of U.S. Pat. No. 2,933,102 discloses a valve where pressurised liquid is used for deforming a flexible hat or top so that a fluid passage is opened through the stem of the valve. This valve, however, is primarily suited for air where there is no risk of clogging the narrow duct in the interior of the stem. Furthermore, there is no possibility of directing the discharged fluid in a desired direction when the valve is opened.